Three-dimensional analysis of the physiologic drift of adjacent teeth following maxillary first premolar extractions.

We assessed the three-dimensional (3D) pattern of the physiologic drift of the remaining adjacent teeth after premolar extraction due to orthodontic reasons and the associated factors. Data were collected from 45 patients aged 17.04 ± 5.14 years who were scheduled to receive a fixed appliance after maxillary premolar extraction. Seventy-five drift models were obtained and digitalized via 3D scanning. The average physiologic drift duration was 81.66 ± 70.03 days. Angular and linear changes in the first molars, second premolars, and canines were measured using the 3D method. All the examined teeth had tipped and moved towards the extraction space, leading to space decreases. Posterior teeth primarily exhibited significant mesial tipping and displacement, without rotation or vertical changes. All canine variables changed, including distal inward rotation and extrusion. The physiologic drift tended to slow over time. Age had a limited negative effect on the mesial drift of posterior teeth, whereas crowding had a limited positive effect on canine drift. Thus, the mesial drift of molars after premolar extraction may lead to molar anchorage loss, particularly among younger patients. The pattern of the physiologic drift of maxillary canines can help relieve crowding and facilitate labially ectopic canine alignment, whereas canine drift is accelerated by more severe crowding.

[The concern and preference of college students in Beijing Haidian district for female maxillary anterior tooth esthetic factors].

OBJECTIVE: To evaluate Beijing college students' concern and preference for maxillary anterior tooth esthetic factors. METHODS: Several images about lip and tooth were made through computer. A questionnaire was sent out to students in ten colleges and then collected. There were five factors to be evaluated: relationship of maxillary incisors and lower lip, numbers of tooth exposed, shape of centric incisor, crown width-length ratio, gingival margin. Concern of the beauty of anterior tooth, ie. tooth shape, tooth arrangement, shape of gingiva and so on, were then analyzed. RESULTS: There were 408 responses collected, and 47.5% (194/408) of them preferred light contact between upper incisors and lower lip; 49.5% (202/408) preferred 8 tooth exposed when smile; 69.1% (282/408) preferred oval crown shape; 52.5% (214/408) preferred 0.85 as a crown width-length ratio; 49.5% (202/408)of responses chose the curve of gingiva runs horizontal. The average score of concern for male was 52.6% (100/190), for female was 59.6% (130/218). CONCLUSIONS: Most results from this study accord with the classical principles of tooth esthetics. Sex affects the concern and preferences of maxillary anterior tooth esthetics factors.